Nitrogen fertilizer added to the soil is readily transformed through a number of undesirable biological and chemical processes, including nitrification, leaching, and evaporation. Many transformation processes reduce the level of nitrogen available for uptake by the targeted plant. One such process is nitrification, a process by which certain widely occurring soil bacteria metabolize the ammonium form of nitrogen in the soil, transforming the nitrogen into nitrite and nitrate forms, which are more susceptible to nitrogen loss through leaching or volatilization via denitrification.
The decrease in available nitrogen due to nitrification necessitates the addition of more nitrogen rich fertilizer to compensate for the loss of agriculturally active nitrogen available to the plants. These concerns intensify the demand for improved management of nitrogen, in order to reduce costs associated with the use of additional nitrogen fertilizer.
Methods for reducing nitrification include treating soil with agriculturally active compounds that inhibit or at least reduce the metabolic activity of at least some microbes in the soil that contribute to nitrification. These compounds include (trichloromethyl)pyridines, such as nitrapyrin, which have been used as nitrification inhibitors in combination with fertilizers as described in U.S. Pat. No. 3,135,594, the disclosure of which is incorporated herein by reference in its entirety. These compounds help to maintain agriculturally-applied ammonium nitrogen in the ammonium form (stabilized nitrogen), thereby enhancing plant growth and crop yield. These compounds have been used efficaciously with a number of plant crops including corn, sorghum, and wheat.
Compounds such as nitrapyrin are unstable in soil in part because they are very volatile. For example, nitrapyrin has a relatively high vapor pressure (2.8×10−3 mm Hg at 23° Celsius), and because of this it has a tendency to volatilize and must be applied immediately or somehow protected from rapid loss after the fertilizer is treated with nitrapyrin. One approach is to add nitrapyrin to a volatile fertilizer, namely anhydrous ammonia, which itself must be added to the soil in a manner that reduces the amount of the volatile active lost to the atmosphere. This method is problematic in that it requires the use of anhydrous ammonia, which is corrosive and must be injected into the soil. This method of applying nitrapyrin, while stabilizing nitrapyrin below the soil surface, is not preferred. This method is unsuitable for many other fertilizer types and their standard application practices such as dry fertilizer granules, which most often are broadcasted onto the soil surface.
Still other approaches to stabilize nitrapyrin and reduce its loss to the atmosphere include applying it to the surface of the soil and then mechanically incorporating it into the soil, or watering it into the soil generally within 8 hours after its application to reduce its loss to the atmosphere. Still another approach is to encapsulate nitrapyrin for rapid or dump release. Such encapsulated forms of nitrapyrin have been formulated with lignin sulfonates as disclosed in U.S. Pat. No. 4,746,513, the disclosure of which is incorporated herein by reference in its entirety. While these formulations are less volatile than simple nitrapyrin, these formulations are better suited for use with liquid urea ammonium nitrate (“UAN”) or liquid manure fertilizers than with dry fertilizers. Although the release of nitrapyrin is delayed by the encapsulation, the capsules release all of the nitrapyrin upon contact with moisture, exhibiting the same stability and volatility disadvantages of the prior application methods.
Another approach to stabilizing nitrapyrin includes polycondensation encapsulation. Additional information regarding this approach can be found in U.S. Pat. No. 5,925,464, the disclosure of which is incorporated herein by reference in its entirety. Some of these formulations enhance handling safety and storage stability of the nitrapyrin using polyurethane rather than polyurea to form at least a portion of the capsule shell.
In some instances, polyurea microencapsulation has been used to produce enhanced nitrification inhibitor compositions for delayed, steady release of nitrification inhibitors for application with fertilizers. Such encapsulated forms of nitrapyrin are disclosed in U.S. Pat. Nos. 8,377,849, 8,741,805, and International application PCT/US15/00217 (publication number WO 2016/108928) the disclosures of which are incorporated herein by reference in their entirety.
There remains a need to deliver nitrification inhibitors such as, for example, (trichloromethyl)pyridines in a more efficient manner and with formulations that provide improved storage stability, as measured by decreased crystal formation over longer periods of time, while maintaining a high level of efficacy comparable to unencapsulated nitrification inhibitors.
While aqueous microcapsule suspensions (a.k.a. capsule suspensions or “CS”) of nitrapyrin (i.e., microencapsulated nitrapyrin) referred to above are more stable than un-encapsulated nitrapyrin in an aqueous solution under certain conditions, it has been observed that crystals of nitrapyrin can form in the aqueous phase of a microcapsule suspension of nitrapyrin. The weight percentage of crystalline nitrapyrin in the bulk aqueous phase of the microcapsule suspension may accumulate over time. Depending upon how the microcapsule suspensions are handled, the presence of measurable levels of crystalline nitrapyrin in the aqueous phase can be of little-to-no consequence or problematic. The presence of even about 0.1 wt. percent crystalline nitrapyrin or above in the aqueous phase of the microcapsule suspension can be especially problematic if the suspension is applied by spraying the suspension through a fine point nozzle with a sprayer containing inline screens.
Additionally, certain commercial embodiments of polyurea microencapsulated nitrification inhibitors, such as, for example, Instinct® and Entrench® (commercial embodiments sold by Dow AgroSciences LLC), are limited by the amount of active ingredient (nitrification inhibitor) that can be microencapsulated and suspended in the aqueous phase without the active ingredient crystallizing into the aqueous phase. For example, in some embodiments, Instinct® and Entrench® include about 17% to about 19% by weight active ingredient (nitrapyrin). Crystallization of the active ingredient into the aqueous phase has limited using increased levels of active ingredient in these aqueous capsule suspensions. Some commercial nitrapyrin capsule suspension formulations have active loadings of 200 g/L, the upper limit of the loading being bound by the solubility of the nitrapyrin in the solvent used inside of the microcapsules.
In some of the inventive embodiments of the present disclosure, no solvent is required to dissolve the nitrapyrin (and/or other active ingredient) in the lipophilic phase. In some embodiments, stable aqueous capsule suspension formulations with up to about 300 g/L nitrapyrin loading are disclosed, without problematic crystallization issues. In some embodiments of the present disclosure, high-load, aqueous, capsule suspension formulations containing nitrapyrin may include those that contain at least about 150 g/L, at least about 200 g/L, at least about 220 g/L, at least about 240 g/L, at least about 260 g/L, at least about 280 g/L, or at least about 300 g/L of microencapsulated nitrapyrin.
Some aspects of the present disclosure include compositions that prevent and/or reduce crystal formation issues observed in aqueous capsule suspension formulations with up to about 300 g/L nitrapyrin loading such as, for example, those that include at least about 150 g/L, at least about 200 g/L, at least about 220 g/L, at least about 240 g/L, at least about 260 g/L, or at least about 280 g/L of microencapsulated nitrapyrin. Crystal formation in nitrification inhibiting compositions can cause problems including filter blockage during field application of the compositions. In some instances, crystals that form in the liquid phase of a capsule suspension are high purity crystals, comprising substantially pure organic nitrification inhibitor, such as, for example, nitrapyrin. In some instances, high purity nitrapyrin (99 wt %) crystals may form in presently available commercial formulations. Crystal formation, in some instances, is dependent upon the temperature of the formulation during handling, storage, and/or transport of the formulations.
In some embodiments of the microcapsule suspension formulations of the present disclosure, stable, high-load, agricultural liquid formulations comprising aqueous microcapsule suspensions containing low melting active ingredients are presented. In some embodiments, the microcapsule suspension formulations are prepared without use of an organic solvent to dissolve the low melting point active such as, for example, a nitrification inhibitor such as nitrapyrin, and may optionally use small amounts of a polymeric ultra-hydrophobe to prepare the microcapsules. In some embodiments, the nitrapyrin containing microcapsule suspension formulation may include a microencapsulated hydrophobic crystal inhibitor additive to prevent or inhibit crystal formation or growth of the nitrapyrin in the aqueous phase. In some embodiments, the nitrapyrin containing microcapsule suspension formulations that include a microencapsulated hydrophobic crystal inhibitor additive provide superior physical, chemical, and/or crystallization stability upon storage, and acceptable volatility and nitrification inhibition attributes in applications to the soil. In some embodiments, the nitrapyrin containing microcapsule suspension formulation containing the microencapsulated hydrophobic crystal inhibitor additive provide superior physical, chemical, and/or crystallization stability upon storage when compared to those formulations containing only a non-microencapsulated hydrophobic crystal inhibitor additive.
In some embodiments of the microcapsule suspension formulations disclosed herein, post addition (i.e. after nitrapyrin microcapsule formation) of a microencapsulated hydrophobic crystal inhibitor additive to the aqueous phase reduces the rate of crystal formation and/or growth in the aqueous phase during storage. In one embodiment, post addition of one or more microencapsulated hydrophobic crystal inhibitor additives provide superior crystal growth inhibition or reduction during storage. In one exemplary embodiment, post-addition of a microencapsulated hydrophobic crystal inhibitor additive that is an aromatic solvent provides superior crystal growth inhibition or reduction in the aqueous phase of the nitrapyrin containing microcapsule suspension formulation.
The present disclosure therefore provides compositions and methods to prevent and/or reduce crystals and crystal formation in high-load, agricultural active compositions containing organic nitrification inhibitors, such as nitrapyrin. In some embodiments, addition of microencapsulated hydrophobic crystal inhibitor additives prevent and/or reduce crystals and crystal formation in capsule suspensions of microencapsulated nitrapyrin better than when using non-microencapsulated hydrophobic crystal inhibitor additives alone. In some embodiments, microencapsulated hydrophobic crystal inhibitor additives provide superior physical stability to high-load, microencapsulated nitrapyrin formulations at from about 15 to about 55° C. storage conditions.
In certain embodiments, in the absence of the addition of one or more microencapsulated hydrophobic crystal inhibitor additives to the aqueous phase and even with the use of a non-microencapsulated hydrophobic crystal inhibitor additive, high-load microcapsule suspension formulations of nitrapyrin may form problematic levels of nitrapyrin crystals in the aqueous phase at temperatures ranging from about 15° C. to about 55° C. These nitrapyrin crystals may be about 99% pure. Over time, such crystals may compose up to 0.5 weight percent or more of the overall microcapsule suspension formulation. These crystals may form at temperatures such as, for example, 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., and 55° C. Microencapsulated solvent-based, hydrophobic crystal inhibitor additives such as aromatic solvents and ester compounds can increase the physical stability of high-load microcapsule suspension formulations of nitrapyrin, by preventing or at least reducing crystal formation in the aqueous phase of the microcapsule suspension formulation.
Illustratively, post-added, microencapsulated aromatic solvents used as hydrophobic crystal inhibitor additives may include: Aromatic 100 Fluid, also known as solvent naphtha or light aromatic; Aromatic 150 Fluid, also known as solvent naphtha, heavy aromatic, high flash aromatic naphtha type II, heavy aromatic solvent naphtha, hydrocarbons, C10 aromatics, >1% naphthalene, A150, S150 (Solvesso 150); and Aromatic 200 Fluid, also known as solvent naphtha, heavy aromatic, high flash aromatic naphtha type II, heavy aromatic solvent naphtha, hydrocarbons, C10-13 aromatics, >1% naphthalene, A200, and S200 (Solvesso 200).
The microencapsulated aromatic solvents used in some embodiments, are naphthalene depleted (“ND”), or contain less than about 1% naphthalene. Said microencapsulated solvents may be added to the microcapsule suspension formulation prior to crystal formation as a preventative measure, or added to the microcapsule suspension formulation after crystal formation as a remedial measure to remove or reduce the presence of crystals.
The ester compounds used in some embodiments as microencapsulated hydrophobic crystal inhibitor additives include: 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate.
Additionally, the microcapsule suspension formulations of the present disclosure can be combined or used in conjunction with pesticides, including arthropodicides, bactericides, fungicides, herbicides, insecticides, miticides, nematicides, nitrification inhibitors such as dicyandiamide, urease inhibitors such as N-(n-butyl) thiophosphoric triamide, and the like or pesticidal mixtures thereof. In such applications, the microcapsule suspension formulation of the present disclosure can be tank mixed with the desired pesticide(s) or they can be applied sequentially.
Disclosed herein is a microcapsule suspension formulation comprising: (a) a first suspended phase of a plurality of microcapsules having a volume median particle size of from about 1 to about 10 microns, wherein the microcapsules include: (1) a microcapsule wall produced by an interfacial polycondensation reaction between a polymeric isocyanate and a polyamine to form a polyurea shell; (2) at least one organic nitrification inhibiting compound encapsulated within the polyurea shell; (b) a second suspended phase of a plurality of microcapsules having a volume median particle size of from about 1 to about 10 microns, wherein the microcapsules include: (1) a microcapsule wall produced by an interfacial polycondensation reaction between a polymeric isocyanate and a polyamine to form a polyurea shell; and (2) at least one hydrophobic crystal inhibitor additive encapsulated within the polyurea shell; and (c) an aqueous phase. In some embodiments, the aqueous phase of the microcapsule suspension formulation may further include at least one additional ingredient selected from the group consisting of: non-encapsulated hydrophobic crystal inhibitor additives, dispersants, emulsifiers, rheology aids, antifoam agents, biocides, antifreeze agents, and mixtures thereof.
In some embodiments, the first suspended phase of the plurality of microcapsules in the formulation include 2-chloro-6-(trichloromethyl)pyridine. In other embodiments, the formulation includes between about 15 weight percent and about 40 weight percent 2-chloro-6-(trichloromethyl)pyridine. Still in other embodiments, the formulation includes between about 0.1 weight percent and about 2.00 weight percent of the at least one polymeric ultra-hydrophobe compound contained within the first suspended phase of the plurality of microcapsules. In some embodiments, the at least one polymeric ultra-hydrophobe compound includes polybutene.
In some exemplary embodiments, the aqueous phase of the microcapsule suspension formulation includes between about 1.0 weight percent and about 10.0 weight percent, between about 2.0 weight percent and about 8.0 weight percent, or between about 3.0 weight percent and about 7.0 weight percent of the hydrophobic crystal inhibitor additive which is encapsulated within the second suspended phase of the plurality of microcapsules. In other exemplary embodiments the hydrophobic crystal inhibitor additive is at least one compound selected from the group consisting of: aromatic solvents such as, for example, naphthalene depleted heavy aromatics, and ester compounds such as, for example, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and mixtures thereof.
In some embodiments, the aqueous phase of the microcapsule suspension formulation includes between about 1.0 weight percent and about 10 weight percent of an emulsifier that is a nonionic polymer surfactant. In some embodiments, the nonionic polymer surfactant is selected from the group consisting of: polyvinyl alcohols.
In some embodiments, the aqueous phase of the microcapsule suspension formulation includes at least one additive selected from the group consisting of: modified styrene acrylic polymeric surfactants (i.e., dispersants), polyvinyl alcohols (i.e., emulsifiers) aqueous emulsion of polydimethylsiloxanes (i.e., antifoam agents), xanthan gums (i.e., rheology aids), microcrystalline celluloses (i.e., rheology aids), sodium carboxymethyl-celluloses (i.e., rheology aids), propylene glycol (i.e., an antifreeze agent), a biocide and mixtures thereof. In other embodiments, the formulation includes between about 40 weight percent and about 70 weight percent of the aqueous phase.
Some aspects of the invention include methods for making a microcapsule suspension formulation comprising the steps of: (a) preparing a lipophilic phase comprising at least one lipophilic isocyanate and at least one polymeric ultra-hydrophobe by mixing said at least one lipophilic isocyanate and at least one polymeric ultra-hydrophobe with at least one molten, low melting-point organic nitrification inhibiting compound; (b) preparing an aqueous phase by dissolving and mixing in water at least one additive selected from the group consisting of: dispersants, emulsifiers, antifoams, biocides, and mixtures thereof; (c) combining the lipophilic phase and aqueous phase to form an oil-in-water emulsion; and (d) combining the oil-in-water emulsion with a solution of at least one polyamine in water to generate microcapsules.
In some embodiments of the method, the lipophilic phase includes 2-chloro-6-(trichloromethyl)pyridine. In other embodiments of the method, the lipophilic phase includes between about 75 weight percent and about 90 weight percent 2-chloro-6-(trichloromethyl)pyridine. In other embodiments of the method, the lipophilic phase includes between about 0.1 weight percent and about 3.00 weight percent of the at least one polymeric ultra-hydrophobe compound. Still in other embodiments of the method, the lipophilic phase includes polybutene (i.e., the polymeric ultra-hydrophobe compound).
In some embodiments, the method further includes the step of: adding at least one additive selected from the group consisting of: dispersants, biocides, an aqueous emulsion of polydimethylsiloxane concentrate, a xanthan gum, a microcrystalline cellulose, a carboxymethyl-cellulose sodium, an anti-freeze additive selected from at least one of ethylene glycol, propylene glycol or glycerol, a non-encapsulated hydrophobic crystal inhibitor additive, an aqueous microcapsule suspension containing a microencapsulated hydrophobic crystal inhibitor additive and mixtures thereof, after the step of combining the oil-in-water emulsion with a solution of at least one polyamine in water to generate microcapsules containing nitrapyrin. In other embodiments of the method, the final microcapsule suspension formulation includes between about 1.0 weight percent and about 10.0 weight percent (on a hydrophobic crystal inhibitor additive weight percent basis) of at least one microencapsulated hydrophobic crystal inhibitor additive. In some exemplary embodiments of the method, the hydrophobic crystal inhibitor additive is at least one compound selected from the group consisting of: aromatic solvents, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and mixtures thereof. In some exemplary embodiments of the method, the hydrophobic crystal inhibitor additive is added to the microcapsule suspension formulation as a second microcapsule suspension whereby the hydrophobic crystal inhibitor additive is contained within the microcapsules of the second microcapsule suspension. In some exemplary embodiments of the method, both microencapsulated and non-microencapsulated hydrophobic crystal inhibitor additive may be added to the microcapsule suspension formulation to prevent or inhibit crystal growth.
In still other embodiments of the method, the aqueous phase includes between about 1.0 weight percent and about 10 weight percent of a nonionic polymer surfactant, and in some embodiments, the nonionic polymer surfactant is selected from the group consisting of: polyvinyl alcohols.
In yet other embodiments of the exemplary method, the final microcapsule suspension includes at least one additive selected from the group consisting of: a modified styrene acrylic polymeric surfactant, an aqueous emulsion of polydimethylsiloxane concentrate, a xanthan gum, a microcrystalline cellulose, a carboxymethyl-cellulose sodium, a biocide, a propylene glycol, and mixtures thereof. In some embodiments, the formulation includes between about 40 weight percent and about 70 weight percent of the aqueous phase. In still other embodiments, the method further includes the step of: controlling the temperature of the oil-in-water emulsion while mixing the lipophilic and aqueous phases to produce oily globules of a desired size.